This invention relates generally to initializing processor-based systems.
Before the operating system is called, the basic input/output system (BIOS) is responsible for initializing and booting the processor-based system. Once the BIOS has completed its tasks, it transfers control to the operating system.
The BIOS may include at least three different levels. The lowest level may be the processor abstraction layer (PAL) that communicates with the hardware and, particularly, the processor. A middle layer is called the system abstraction layer (SAL). The SAL may attempt to correct correctable errors after they are detected and reported by the PAL. The uppermost layer, called the extensible firmware interface (EFI), communicates with the operating system and, in fact, launches the operating system.
In some processor-based systems, more than one PAL component may be provided. For example, in one implementation, two processor-specific components, which may be denominated PAL_A_SPECIFIC and PAL-B, may be provided. These two processor-specific components may typically be stored in system flash and may have a functionality akin to that normally handled by microcode. A third component called PAL_A_GENERIC is processor-independent and is the first component to execute in response to a restart event in some architectures.
The PAL_A_GENERIC component searches a firmware interface table (FIT) to locate a suitable onboard processor compatible with PAL_A_SPECIFIC and authenticates the component. The FIT, also stored in system flash, contains starting addresses and sizes for firmware components outside the protected boot block. The PAL_A_SPECIFIC authenticates the PAL-B component. The PAL_A_SPECIFIC then discovers the PAL-B through a FIT constructed by the original equipment manufacturer detailing, where in the system flash, PAL-B can be found.
After authentication, the PAL_A_SPECIFIC passes control to the original equipment manufacturer provided SAL-A component code. The control flow at this point can be recovery in the case of failed signature verification of the PAL-B or in the case of an incompatible PAL-B with respect to a particular processor stepping.
Only a single PAL-B component is supported because of flash memory space constraints. When it is desired to update the PAL-B in system flash with a newer version of PAL-B, the customer may use a so-called crisis recovery flow. The crisis recovery flow entails user intervention including flipping jumper switches and inserting a disk.
Thus, there is a need for a way that enables updating of PAL components without the need for user intervention.